Machines for cutting hard surfaces, such as used in the trenching and mining industries and for highway cold planning to remove the upper surface of concrete and asphalt pavement, employ tools fitted into tool holders on a rotating wheel or drum. The tools have a tapered forward cutting end and axially located behind the cutting end is a cylindrical shank that rotatably fits within a complementarily shaped bore in the tool holder. Such rotatable tools have an annular rearwardly directed flange between the forward cutting end and the shank that contacts the forward surface of the tool holder. Force is applied by the tool holder against the radial flange to force the tool into the hard surface to be cut. The shank is retained in the bore of the tool holder by a sleeve made of spring steel so as to be compressible and has an unstressed diameter greater than that of the bore such that the compression of the sleeve retains the sleeve within the bore of the tool holder. To prevent the withdrawal of the tool from the sleeve inwardly directed projections on the inner surface of the sleeve engage one or more annular rings around the circumference of the shank of the tool.
To maximize the useful life of such tools, the tools are adapted to rotate around the axis of the shank thereby causing the tool to wear evenly around its circumference. A tool in a machine may go through 50,000 rotations or more during a single workday. Where the annular rearwardly directed flange of the tool rotates against the forward surface of the tool holder, the rotation of the tool will, over a period of time, cause the forward surface of the tool holder to become worn away. To prevent such wear, it is common to provide an annular wear ring around the shank of the tool between the forward surface of the tool holder and the rearwardly directed flange of the tool.
When the wear ring operates properly, the wear ring remains stationary against the forward surface of the tool holder while the tool rotates against the surface of the wear ring such that only the forward surface of the wear ring becomes worn. Tool rotation occurs because the tool is mounted at an angle of about seven degrees from a plane perpendicular to the axis of rotation of the drum or wheel. As a result of the angle, when the tool impacts against a surface to be cut, there is a component of force applied to the outer surface of the tool that is perpendicular to the axis of rotation. Some of this force is applied to the outer circumference of the wear ring and, as a result, to some degree the wear ring rotates with the tool rather than remaining stationary with the tool holder. When this occurs the wear ring, which is intended to protect the forward end of the tool holder, causes wear to the surface it was intended to protect. It would be desirable, therefore, to provide an improved wear ring that would be locked against rotation with the tool during the operation of the machine.